A portable, self-retaining apparatus, system and method for mixing fluids in a container is disclosed. The self-retaining, portable fluid mixing apparatus is capable of being connected to a container and retained thereon without the aid of a user during use. The self-retaining fluid mixing device, system and method of the disclosure may be used in various capacities to mix a wide variety of fluids having a wide variety of viscosities. Thus, the disclosure is not limited to any particular type of fluid or viscosity, but an example of the fluids that may be mixed include flavoring syrups and thickeners used for shaved ice confectioneries. The mixer or apparatus can be quickly attached to and detached from a container without the use of extraneous, cumbersome fasteners. The torque caused by operation of the motor causes the apparatus and system to lock in place during use, such that when the torque is released, the apparatus may be quickly and easily removed from the container.